The present invention relates to a pressure roll for a web of fibers, such as a paper web, and more particularly to a roll of stone or a like material, which uses hydraulic pressure to transmit a pressing force to a stationary beam.
An example of a pressure roll for a web of fibers may be found in U.S. Pat. No. 4,414,890. This roll utilizes a predominantly metallic roll shell, whose bearing structure is made from a metal pipe. The metal roll shell can come into direct contact with the web of fibers. In some applications, however, a blanket, for instance of rubber, covers the metal roll shell. Although rolls of this type have proven their worth, they are not suitable for the dewatering press in all paper machines. For example, in paper manufacture using wood pulp as a raw material, the surface of the roll which is contacted by the wet paper web must be formed of stone, preferably a natural stone, such as granite, although an equivalent artificial stone may be used. Heretofore, this has generally only been possible by having substantially the entire body of the roll consist of stone.
A stone roll of this type is disclosed in U.S. Pat. No. 4,272,873. This roll has a body made of stone which is either in the form of a tubular roll shell or is solid. For both roll forms, disk-shaped roll axial stressing flanges are arranged on the end surfaces of the roll. A plurality of stressing rods connect the flanges to stress the stone roll body in the axial direction. This axial stress assures that upon exertion of radially directed pressure on the roll body, in cooperation with a mating roll, excessively high bending stresses which might destroy the stone roll body in the circumferential region remote from the mating roll may be avoided. One significant disadvantage of these known stone rolls however, is that despite the prestressing of the stone roll body, only relatively slight pressing force per unit of length is permissible.